1. Field of the Invention
The present invention relates to a gas-pressure-driven apparatus which moves a movable member in relation to a main body thereof in accordance with the pressure of a working chamber to which a working gas is supplied and from which the working gas is discharged.
2. Description of the Related Art
Conventionally, there has been known a method for calculating the moved position and movement amount of a piston (i.e., a movable member) in a hydraulic cylinder on the basis of the flow rate of pressurized fluid (see, e.g., Japanese Patent Gazette No. 5331986). Since the method disclosed in Japanese Patent Gazette No. 5331986 monitors the integrated flow rate of the pressurized fluid whose integration starts from a state in which the piston has stopped at its initial position, even when the piston stops at an intermediate position between the initial position and a displacement end position, the intermediate position to which the piston has moved can be detected.
However, the method disclosed in Japanese Patent Gazette No. 5331986 cannot determine the initial position of the piston in the case where the initial position of the piston is not one of the displacement end positions; i.e., opposite ends of the movement range of the piston. In such a case, the moved position of the piston (which correlates with the volume of the working chamber) cannot be calculated.